(1) Field of the Invention
The present invention relates to a method and system for testing a specimen such as an automatic power transmission of a vehicle and analyzing an engine output characteristic (for example, an input torque of the power transmission) via the specimen to be tested using a dynamometer (i.e., a low inertia driving unit). The present invention, more particularly, relates to the method and system in which the engine output characteristic is estimated using, e.g., a low inertia driving unit when testing since the engine output characteristic cannot actually be measured in a system in which the engine and specimen are connected together.
(2) Background of the Art
It is necessary to grasp an engine output characteristics in analyzing and evaluating characteristics of power transmissions to be installed in automotive vehicles and for general troubleshooting for automatic transmissions. Therefore, although testing is carried out with the automotive power transmission as a specimen connected to a vehicular engine, it is difficult in construction to insert a torque meter between the engine and the power transmission. Consequently, an accurate measurement of torque of an input shaft of the power transmission cannot be made. To cope with such a problem described above, the engine output characteristic data supplied from an engine manufacturer has been used when evaluating a performance of the power transmission.
However, since it cannot be accurately determined whether the actual output of the engine connected to the power transmission coincides with the derived output characteristic data, high reliability cannot rest on the obtained result.
In addition, in transient performance testing of the power transmission, with a specimen power transmission connected to an engine, output control of the engine is carried out to test acceleration/deceleration endurance and gear shift `feel` of the power transmission.
In such an engine driving method as described above, it is difficult to repeatedly reproduce the same engine operating conditions. Consequently, a motor driving method has been adopted. In a transient dynamometer used in the motor driving method, a low inertia driving unit having a low inertia equal to or more than that of the engine and the same output characteristic transient is used to realize a large change of speed during gear shift operation.
FIG. 9 shows a previously proposed transient dynamometer (as shown in a U.S. patent application Ser. No. 427,031 filed on Oct. 25, 1989), now U.S. Pat. No. 5,060,176.
The low inertia driving unit (TR-DY) 1 includes a low inertia DC motor and a speed governor. The DC motor performs a torque control or speed control as a current control minor loop of a thyristor reonard method to obtain a low inertia output equal to or more than the engine. An axial output of the drive unit 1 provides a drive source for a specimen of a power transmission (AT) 3 via an axial torque meter 2. The axial output of the specimen automatic transmission (AT) 3 serves as a driving force for an energy absorbing dynamometer (DY) 5 and flywheel 5A via a torque meter (TM) 4. The low inertia driving unit 1, specimen automatic transmission 3, and energy absorbing dynamometer 5 are respectively provided with self-contained control units 6, 7, and 8.
The TR-DY control unit 6 carries out a torque or speed control of the low inertia driving unit 1 in response to a torque or speed command. In the torque control, a feedback control is carried out by comparing the torque command derived from an engine characteristic generator 9 with the detected torque T.sub.1 of the torque meter 2. On the other hand, for speed control, feedback control is carried out by comparing the speed command with the detected speed N.sub.1 of the speed detector 10.
The engine characteristic generator 9 constituted by a microcomputer has a data such that an actual engine output torque T versus speed N characteristic is set or measured for each opening angle .theta..sub.i of an engine throttle valve. Then, the engine characteristic generator 9 derives a torque to be output by the low inertia drive unit 1 from the input opening angle of the throttle valve and from the speed detected value N.sub.1 so as to provide the torque command output. It is noted that although the opening angle of the throttle valve .theta..sub.i can be used in place of an engine intake negative pressure, the opening angle of the throttle valve .theta..sub.i is herein used.
In the previously proposed transient dynamometer, the engine characteristic generator 9 carries out data collection through an analysis of the actual engine output characteristic.
In order to coincide with a behavior of an actual vehicle during the analysis of the engine output characteristic, a testing arrangement may be considered in which the torque meter, energy absorbing dynamometer, and flywheel (both absorbing dynamometer and flywheel providing a pesudo load to the power transmission) are connected to the power transmission (refer to FIG. 1 (B)). However, it is difficult to directly measure the output characteristic (torque output T.sub.1) by means of the action of a torque converter of the automatic transmission. Therefore, a method for measuring the engine output from the torque meter in a shifted state of a four-speed (gear shift ratio of 1:1) manual transmission with a manual transmission connected in place of an automatic transmission has been adopted. However a manual transmission which matches the engine is not always prepared. Actually, it is often impossible to accurately measure the engine output characteristic.
As described above, although the output characteristic data for the engine itself derived from the engine manufacturer may be used, the data may be different from the actual output characteristic data with the automatic transmission and load connected.